1. Field of the Invention
This invention relates to a method of film formation and a method for manufacturing a semiconductor device in which, when a silicon oxide film (a NSG film: a Non-doped Silicate Glass) is formed on a substrate having a recess by a CVD method using a mixed gas containing TEOS and ozone, surface dependency of the substrate is eliminated, whereby a silicon oxide film flows into the recess of the surface.
The surface dependency is defined as a property of a surface such that film formation depends on the property of the surface on which the film is deposited.
2. Description of the Prior Art
In recent years, micronizing has been advanced for semiconductor devices. Recesses narrow in width and deeper in depth such as the recess between wirings and the recess in which an insulating material is embedded for an insulating element separation, are designed to be formed on a semiconductor substrate surface. In such semiconductor devices, an insulating film is required to become embedded in the recess.
Therefore, a silicon oxide film excellent in film quality (hereinafter referred to as a High O3/TEOS SiO2 film) is required to be formed and to become embedded in the recess without leaving a clearance. A CVD method is used as a method of the film formation. Mixed gas containing both the TEOS (Tetraethylorthosilicate) and the ozone-containing gas containing a high concentration of O3 is used as a deposition gas, said ozone-containing gas containing 1% or more O3 in O2.
However, since the High O3/TEOS SiO2 film is sensitive to a property of the surface of the substrate, the depositing film tends to be influenced by that surface property. The influence of the surface dependency appears as a reduction in the film formation rate, as surface roughness of the depositing film and as a reduction in film quality. Therefore, in order to deposit the High O3/TEOS SiO2 film on a silicon substrate with the same film formation rate, surface condition of the depositing film and film quality of the depositing film, it is required for the surface of the substrate be such that the film formation of the High O3/TEOS SiO2 film not be influenced by surface dependency. Heretofore, in order to eliminate such surface dependency, the following countermeasures are have been taken:
{circle around (1)} The silicon oxide film is formed as a base layer on the surface of the substrate by a plasma enhanced CVD. This is disclosed in Japanese Laid-open Patent Publication No. Hei. 7-211712.
{circle around (2)} The surface of the substrate is exposed to plasma gases. This is disclosed in Japanese Laid-open Patent Publication No. Hei. 4-94539.
{circle around (3)} The silicon oxide film hereinafter referred to as a Low O3/TEOS SiO2 film) is formed as a base layer on the surface of the substrate by the CVD method. As the film formation gas, the reaction gas containing the ozone-containing gas containing low concentration O3 whose the concentration of O3 in O2 is less than 1% and TEOS is used. This is disclosed in Japanese Laid-open Patent Publication No. Hei. 3-198340.
Furthermore, the following method combining the methods described above has been used.
{circle around (4)} Low O3/TEOS SiO2 film is formed as the base layer on the surface of the substrate by the CVD method and subsequently, the Low O3/TEOS SiO2 film is exposed to plasma gases. A reaction gas containing both the TEOS and a low ozone-containing gas such that the concentration of O3 in O2 is as low as less than 1% is used as the film formation gas for the Low O3/TEOS SiO2 film.
{circle around (5)} The High O3/TEOS SiO2 film is formed as the base layer on the surface of the substrate by the CVD method and subsequently, the High O3/TEOS SiO2 film is exposed to plasma gases. A reaction gas containing both the TEOS and a high ozone-containing gas such that the concentration of O3 in O2 is as high as not less than 1% is used as the film formation gas for the High O3/TEOS SiO2 film.
Additional methods for eliminating the surface dependency of the substrate are disclosed in Japanese Laid-open Patent Publication No. Hei. 7-66131.
By adoption of such methods, the O3/TEOS SiO2 depositing film is not influenced by surface dependency of the substrate and has sufficient fluidity.
However, in the methods for eliminating the surface dependency described above, there are the following problems:
That is, in the method forming the silicon oxide film as the base layer on the surface of the substrate by the CVD method described as {circle around (1)} above, since the silicon oxide film formed by the plasma enhanced CVD method is poor in step coverage, it is not suitable for embedding a recess narrow in width and deeper in depth.
Moreover, in the method described as {circle around (2)} above, involving exposing the surface of the substrate to plasma gases, since a plasma apparatus is required, the apparatus becomes expensive. Moreover, in such method, there are other problems that lead to an increase in cost and it is a question whether or not reform can be performed to the bottom of a recess narrow in width and deeper in depth by the plasma.
Furthermore, in the method described as {circle around (3)}, the thickness of the Low O3/TEOS SiO2film is required at least 50 nm or more. It is not suitable for embedding a recess narrow in width and deeper in depth.
Moreover, with regard to the item {circle around (4)} and the item {circle around (5)} also, there are the same problems as associated with the item {circle around (2)} and the item {circle around (3)}.
It is the object of this invention to provide a method of film formation and a method for manufacturing a semiconductor device capable of reliably eliminating the surface dependency of the substrate, to form an insulating film having excellent film quality.
The object of this invention is to provide a method of film formation and a method for manufacturing a semiconductor device capable of embedding the insulating film, without clearance, in a recess of the substrate, wherein the recess is narrow in width and deeper in depth.
As described above, in this invention, a phosphorus-containing insulating film such as a phosphosilicate glass film is formed as a base layer on the surface of the substrate. Furthermore, on the phosphorus-containing insulating film, a silicon-containing insulating film is formed by a chemical vapor film formation using the mixed gas containing the ozone-containing gas and a silicon-containing gas.
According to experiments by the inventor, in the case of depositing the silicon-containing insulating film by a chemical vapor deposition method using the mixed gas containing the ozone containing gas and a silicon-containing gas on the substrate, the surface dependency of the substrate can be eliminated by precoating the surface of the substrate with a phosphorus-containing insulating film such as a phosphosilicate glass film (a PSG film) or a borophosphosilicate glass film (BPSG film).
Incidentally, it has been stated that, when the High O3/TEOS SiO2film is formed by the chemical vapor deposition method using the ozone-containing gas and a silicon-containing gas containing high concentration ozone (defined as a concentration of ozone in oxygen of 1% or more), the surface dependency of the deposition film on the substrate is remarkably apparent. According to the invention, since the surface dependency can be eliminated by precoating the surface of the substrate with a phosphorus-containing insulating film, sufficient fluidity can be obtained, even when the High O3/TEOS SiO2 film is readily influenced by the surface dependency is deposited.
Moreover, the surface dependency can be sufficiently eliminated by a phosphorus-containing insulating film with a thin film thickness of approximate 10 nm. Therefore, even the inside of a narrow recess of, at least approximately 20 nm or more in width can be coated. Moreover, the upper limit of the film thickness of the phosphorus-containing insulating film is influenced by the width of the recess. At this point of time, the film thickness of the phosphorus-containing insulating film is defined preferably such that the film thickness of the phosphorus-containing insulating film becomes sufficiently thin as compared with the silicon-containing insulating film, in an interlayer dielectric film constituted by the phosphorus containing insulating film as the base layer and the silicon containing insulating film which lies thereon. Usually, a phosphorus-containing insulating film having a thickness of approximately 100 nm is acceptable.
Therefore, when there is a recess narrow in width and deeper in depth on the surface of the substrate, the recess can be embedded with the silicon oxide film without clearance, and without generating voids and seams on the silicon oxide film formed in the recess.
In this case, the ozone-containing gas, the silicon-containing gas and the phosphorus-containing gas are discharged by a first gas discharge means to form the phosphorus-containing insulating film and then the ozone-containing gas and the silicon-containing gas are discharged by a second gas discharge means continuously, after ceasing the discharge by the first discharge means, to form the silicon oxide film. Incidentally, it has been found by experiment that, in order to eliminate the dependency on the surface of the phosphorus-containing insulating film, when subsequently forming the silicon-containing insulating film on the phosphorus-containing insulating film, it is required that there be no phosphorus-containing gas in the reaction gas. That is when the silicon-containing insulating film is formed using a gas discharge means which differs from the gas discharge means where forming the phosphorus-containing insulating film, the surface dependency at the surface of the phosphorus-containing insulating film can be eliminated. A deposition chamber for the phosphorus-containing insulating film may be replaced with a deposition chamber for the silicon-containing insulating film or the alternate gas discharge means may be switched respectively upon forming also.
Moreover, the following fact has been verified by experiment. After the process of forming the phosphorus-containing insulating film and before the process of forming the silicon-containing insulating film on the phosphorus-containing insulating film, the surface of the phosphorus-containing insulating film is exposed to the atmosphere, or the surface of the phosphorus-containing insulating film is exposed to water vapor while heating the surface of the phosphorus-containing insulating film, the surface of the phosphorus-containing insulating film is converted to hydrophobic, and when the surface of the phosphorus-containing insulating film is converted to hydrophobic, the surface dependency in the above-described film deposition is suppressed. Especially, when the High O3/TEOS SiO2 film readily influenced by the surface dependency is deposited, such treatment is preferably performed.
Furthermore, the ozone-containing gas used in the film formation of the silicon-containing insulating film is the gas containing ozone of the concentration of less than 10% in oxygen.
As described above, to use the phosphorus-containing insulating film as the base layer is effective, in particular, when depositing the High O3/TEOS SiO2 film readily influenced by the surface dependency, using the high ozone-containing gas wherein the concentration of ozone in oxygen is as high as 1% or more.
As a matter of course, this is effective also when depositing the silicon oxide film (the Low O3/TEOS SiO2 film) not readily influenced by the surface dependency using the low ozone containing gas wherein the concentration of ozone in oxygen is as low as less than 1%.
The reason why is that, by the deposition, penetration of moisture and migration of alkali ions from the Low O3/TEOS SiO2 film to the substrate can be prevented.
In the case of depositing the silicon-containing insulating film by CVD method using the mixed gas of the O3/TEOS, the flowability of the depositing film can be increased by regulating the deposition temperature within the range of 350xc2x0 C. to 550xc2x0 C. With regard to the deposition temperature, in order to obtain sufficient flowability of the depositing film, it is preferable that the deposition temperature be regulated within the range of 375xc2x0 C. to 425xc2x0 C.